This invention relates to manufacturing optical fibre, particularly to the automatic control of the manufacturing process.
High quality optical fibre for transmission systems needs to have the mechanical properties sufficient to withstand stresses to which it is subjected in use. A typical fibre has an outside diameter of 125 microns and is drawn from a glass preform of about 17 mm diameter and about 1.0 m long. Conventionally the optical fibre preform is inserted slowly into a furnace which melts the end of the preform from which is drawn the optical fibre. The preform is held in a chuck which is driven by a precision drive motor and lead screw which feeds the preform at a slow, predetermined rate in to the furnace.
Not all the preform can be converted into optical fibre partly because end portions of the preform do not have a uniform diameter and partly because that end portion of the preform which is held in the chuck cannot easily be released for melting in order to manufacture the optical fibre. It is therefore necessary for the operator of the optical fibre pulling tower to judge when the useful portion of the optical fibre preform has been drawn, and at that point to shut down the pulling process by shutting down the furnace, stopping the capstan and withdrawing the remainder of the preform out of the furnace.
In commencing the process the tip of the preform is inserted into the furnace which has in the meantime been run up to operating temperature, and as the first portion of optical fibre appears from underneath the furnace it is slowly fed down through the various stages of the pulling process, including fibre diameter measuring device, coating applicator coating curing stage and onto the capstan. This initial start-up procedure is difficult to do manually and relies heavily on the expertise of the operator and it is an object of the present invention to alleviate these difficulties.